Nutrition

Does 16:8 Intermittent Fasting Work For Fat Loss?

Intermittent fasting has gotten to be such a popular topic and a relatively popular practice over the last several years.

As I continue to learn more and more about it from different people, from different research, and from my own experience, I wanted to share where I currently stand with it.

I wanted to share my thoughts on fasting from a few angles like why or why not to do it. Who is intermittent fasting for and not for. What does the science say about it. And how long should you fast or not fast for.

Let’s start by defining what fasting is.

Fasting is defined as abstaining from food or certain drinks for a particular period of time. 

A common interval of fasting that is discussed and commonly implemented is the 16:8 fast. Meaning you don’t eat for 16 hours, and then you have an 8-hour feeding window. This could look like finishing dinner by 6pm one night and then the next day you don’t eat until 10am.

But, do you know why it’s 16:8? Or how the 16:8 feeding window came about?

It’s because a graduate student who ran studies on fasting had a girlfriend who said, look, you can be in the lab 10 hours a day but you can’t be in the lab for 14 hours a day if you want this relationship to work. And so this guy himself had about 8 hours during the day where he could eat.

And so the 8-hour feeding window was simply born out of the relationship this guy had and how he had to make it work into his lifestyle. There’s nothing magical per say about the numbers 16 and 8. 

So, while a lot of people hold that number as holy, it wasn’t born out of any specific research that shows that at the 16-hour mark something magical happens. That doesn’t mean that the 16:8 fast is not useful for fat loss but I just wanted to provide you with some context first.

And nowadays some people have started to do much longer fasts like 24 hours, 3 days, and even 7 days.

Why are people doing this and why would you fast in the first place?

The people who are for intermittent fasting do it for a few reasons.

1. Fat Burning

The idea is that if you go a long enough period of time without eating, then your body will deplete its glycogen stores. This means that your body no longer has glucose to run off of, so it has to transition to burning fat for energy. And therefore you have the ability to burn excess body fat.

While this is true, some people say that if equated for calories, there is no difference in the amount of body fat you will burn if you fast vs. if you simply eat less at each meal, again, if equated for calories.

2. Cognitive Benefits

A lot of people report more mental clarity and alertness when they are fasting. 

The mechanism that could be behind this is that some people say that fat is the brain’s preferred energy source - ketones in particular.

And so if you are getting into a state of ketosis and your body is producing ketones, then your brain will operate more effectively.

In my anecdotal experience, I do believe that I’ve experienced greater levels of focus while fasting. Whether that’s due to the ketones being the brain’s preferred energy source or simply a factor of not needing to break up my work to go eat, I’m not sure.

But there may be good cause to experiment with this to see what your results are.

3. Autophagy

Autophagy, simply put, is cellular death. The idea is that when you put your body in starvation mode through fasting, the damaged cells will die off so that new ones can replace them.

I think there can be a lot of merit to autophagy when it comes to fasting but a lot of people debate when autophagy really starts occurring inside the body. 

There’s no doubt that the longer you fast, the more autophagy will take place.

There are other people who say that again, if equated for calories, caloric restriction over time provides the same level of autophagy that fasting does.

So whether or not it’s fasting that leads to autophagy or simply eating less is up for debate.

However, I do believe that long fasts, done every once in a while, can provide benefits from the standpoint of cellular death and repair.

4. Improving Insulin Sensitivity 

The way in which your cells respond to insulin is a big factor in health. If you are healthy, you are said to be more insulin sensitive. This means that your cells are more receptive to insulin binding to them and transporting glucose inside the cells for energy.

If you are unhealthy, you are said to be more insulin resistant. This means that your cells are less receptive to insulin, not allowing glucose inside the cell, leading to excess glucose and insulin in the bloodstream.

Fasting is said to improve insulin sensitivity because when you don’t eat, your body won’t be triggered to produce insulin. Because insulin is produced when glucose enters the body.

Now that we know the potential benefits of fasting, let’s talk about who fasting is for and maybe not for.

Who Is Fasting For?

If you’re currently eating a very unhealthy diet, then fasting can provide some immediate benefits. Because if you go from eating 3 unhealthy meals a day, to eating 2 unhealthy meals a day, then yes, you’ll look and feel better.

But it’s not necessarily because of the fast in and of itself, it’s more because of the fact that you’re eating less crappy food.

I believe fasting can be a great tool if you:
- Have excess body fat 
- Are insulin resistant
- Do well with clear and defined boundaries
- Have a healthy enough relationship with food and/or
- Are wanting to experiment with it

Let’s go through them one by one.

Excess Body Fat

I think fasting can be a great tool to help burn excess body fat because of its ability to easily put you in a caloric deficit - eating less calories than you burn.

However, if you fast repeatedly, week after week, month after month, and year after year, I do believe there’s a chance you can slow down your metabolism making it easier to put on body fat if you ever stop fasting. Keep that in mind. 

Insulin Resistant

You’re probably insulin resistant if you have high blood glucose and blood insulin levels, which you can learn from a blood test.

If that’s the case, if you implement intermittent fasting for a few weeks to a couple months and then get more blood work done, there’s a good possibility that your numbers will look healthier.

Clear and Defined Boundaries

If you do well with clear and defined boundaries, intermittent fasting might be a good tool for you. Let’s say that your goal is to lose body fat, and you know you need to eat less in order to do so. Some people do well with eating less at each meal, but you might like just eating for less hours of the day.

So, if you think it’s easier to eat less by simply saying that I’m not going to eat between this hour and this hour, then fasting may be a good tool for you.

A Healthy Relationship With Food

I do think that a potential big downfall of fasting can be what it does with your relationship with food. Fasting can lead some people to the conclusion that:

Eating = Bad
Not Eating = Good

That can lead to a restrictive mindset and a dangerous relationship with food.

For that reason, if your current relationship with food is shoddy, then you may want to stay wary of fasting.

Experimentation

If you’re wanting to experiment with fasting for any reason, then from a physiological perspective the only downside I see is that you do have the ability to lose some muscle if you’re in a prolonged calorie deficit.

Other than that downside and the downside of potentially harming your relationship with food, then there’s not much reason to be concerned about fasting.

I think it can be a great tool to lose body fat, and there may be more and more science that comes out that shows its longevity and anti-aging benefits as well.

Let’s finish with my protocol. 

My Fasting Protocol

Fasting 12 hours every night is a good idea for basically everyone. Meaning if you finish eating at 8pm, then don’t eat the next morning until 8am. 

Most people are completely fine experimenting with a 12-16 hour fast as well.

Implementing a 12-16 hour fast can be a great tool for fat loss because it can help you eat less calories putting you in a caloric deficit. But the danger comes in when you are constantly eating too few calories therefore slowing down your metabolism. 

So, when you implement fasting don’t do it all the time and don’t do it excessively so as to keep your metabolism fast.

If you want to go longer than a 16 hour fast, then there may be some benefits for insulin sensitivity and autophagy but know that if done excessively you may lose muscle mass and slow down your metabolism.

I’d recommend that if you’re doing 16+ hour fasts, then do them periodically, not religiously. 

Lastly, now this is not my area of expertise, but some believe and have shown that fasting can have negative side effects to female hormone levels. This is something that I plan on exploring and learning more about in the near future.

In addition, if you are pregnant, fasting is not a good idea for you.

And as always, seek out your primary care doctor before making any big changes.

I hope today provides you with some more insight into fasting. Why you might do it or not do it, who it might be for, and how long to do it or not do it.

I think fasting can be great for some and not great for others.

Like anything with our health there is not a one-size-fits-all approach.

It always depends. Context and personalization is required.

To getting closer to your Best You,

Nick

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